This invention relates to an electrode for use in monitoring electrical body signals and more particularly to a disposable, pre-gelled, self-prepping electrode.
Disposable electrodes applied to the skin are used extensively in the monitoring of electrical activity of body functions. The most widely used electrodes require that the skin be prepared before applying the electrode in order to get good electrical contact. This is usually accomplished by first wiping the skin with alcohol to remove dirt and oils. The skin is then further prepared by abrading the electrode sites with a grit-impregnated solution on a cotton swab or with some other abrasive means to remove the outer layers of skin which generally cause poor electrical contact. The electrodes are then applied to the prepared sites in contact with blood-enriched skin layers, thereby giving a relatively low electrical contact impedance.
Many of the pre-gelled electrodes that are widely used in medical monitoring of electrical body signals are disposable, pre-gelled electrodes. Examples of such electrodes are shown and described in U.S. Pat. No. 3,805,769 issued to Sessions; U.S. Pat. No. 3,828,766 issued to Krasnow; U.S. Pat. No. 4,029,086 issued to Corasanti; U.S. Pat. No. 4,640,289 issued to Craighead; and U.S. Pat. No. 4,945,911 issued to Cohen. These electrodes, however, all require multiple, separate and time consuming steps of skin preparation, to reduce the contact impedance with the skin before they are applied to the body.
To reduce the number of steps required to prepare the skin, several self-preparing electrodes have been developed. U.S. Pat. No. 4,027,664 issued to Heavner describes an electrode having a cover with an abrasive surface to give the applicator of the electrode a ready means to abrade and prepare the skin before application of the electrode. The abrasive means is discarded after application. U.S. Pat. No. 4,995,392 issued to Sherwin utilizes a removable, non-conductive brush through the center of a reusable electrode to perform the skin preparation. U.S. Pat. No. 3,774,592 issued to Lahr utilizes an electrode with an absorbent pad placed against the skin through which a separate stiff-bristled brush is dabbed to micropuncture the skin to prepare it.
Each of the techniques described above also require multiple, separate components or steps to perform the skin preparation even though they are "self-preparing". In many situations in patient monitoring, keeping physical track of multiple, separate components is inconvenient because of the clutter or haste typical, for example, of an operating room or intensive care unit. Requiring separate steps to perform skin preparation makes it difficult to improve contact impedance once the electrode has been applied to the patient or after a medical procedure is underway. If the preparation was inadequate, once the electrode has been applied it must be removed, the skin reabraded, and most likely a new electrode would have to be reapplied, adding additional expense to the additional preparation time. Too much abrasion can cause a skin injury or bleeding, leaving the patient with a lasting wound. Also, when an abrading means incorporated as part of an electrode cover or another separate mechanical abrader is used, it is likely that the results will be varied from patient to patient since the results are dependent upon the type of skin of the patient and the abrading technique used by the person applying the electrode.
U.S. Pat. No. 4,274,419 issued to Tam utilizes a separate hand-held mechanical rotating apparatus to rotate a center abrasive disk which is part of an electrode that spins against the skin and continuously measures skin contact impedance. This technique may give more consistent impedance results, but the need for a rotating apparatus (or separate brushes as described above) to perform skin preparation is also a recurring expense in the case of the brushes which generally cannot be reused, and a very high one-time expense in the case of the rotating apparatus. Such a mechanical abrading device is also prone to cause abrasion skin injuries.
U.S. Pat. No. 4,706,679 issued to Schmidt utilizes a metallic brush similar in function to the one used in U.S. Pat. No. 4,995,392 but that remains in contact with the patient during use. Metal in direct contact with the patient's skin causes chemical half-cell reactions that generate offset voltages at the points of contact, interfering with the sensitive measurement of the low signal voltages of the body.
The application of several electrodes, which is typical for medical monitoring, is very time consuming using known methods because of the steps required and the uncertainty of the skin preparation results. Also, all of the known preparation devices, because of the need to physically handle the multiple, separate items required to prepare the skin, cause risk to the applicator by potential contact with blood and by possible disease transmittal during preparation.
It is therefore a principal object of the present invention to provide a self-prepping electrode which easily and reliably prepares the skin to assume a relatively low electrical contact impedance.
Another object of the present invention is to provide a self-prepping electrode which can prepare the skin without requiring the use of more than one component to be handled by the person applying the electrode.
A still further object of the present invention is to provide a self-prepping electrode which minimizes the chances of the occurrence of any skin abrasion injuries.